The present invention relates to gas metal arc welding torches of the general type disclosed, for example, in U.S. Pat. Nos. 2,769,894, No. 2,836,705, No. 3,048,691 and No. 3,226,526, and more specifically, to welding nozzles which are used on torches for gas metal arc welding.
There are three conventional methods of Gas Metal Arc Welding, previously known as Metal Inert Gas (MIG), for transferring welding wire to the weld. These methods are globular, short arc, and spray transfer. Globular type metal transfer across the arc occurs in large, irregular shaped droplets. This type of metal transfer commonly uses shielding gasses consisting of CO.sub.2 mixtures and has a disadvantage in that it produces an erratic arc and generates considerable weld spatter. In the short arc method of metal transfer, no metal transfers across the arc. Instead, metal transfer occurs when the electrode wire makes contact with the metal being welded. Shielding gases commonly used with this process are welding grade CO.sub.2, argon-CO.sub.2 mixtures and argon-oxygen mixtures. Although this type of metal transfer reduces the amount of weld spatter generated by the arc, spatter is still a major problem.
Spray type metal transfer is accomplished by the movement of a stream of small droplets across the arc from the electrode to the metal piece being welded. This type of metal transfer usually employs relatively high voltages and currents. The shielding gases used for this type of weld transfer are usually argon-CO.sub.2, argon-oxygen or a combination of argon-CO.sub.2 -oxygen. Spray type metal transfer produces the least amount of weld spatter of the three basic techniques, but this method requires careful control of the shielding gas mixture. Without proper control, or due to an inexperienced operator or antiquated equipment, even spray type metal transfer can produce weld spatter in the same magnitude as the globular and short arc welds.
When producing a MIG weld in an inert environment, the molten material or spatter adheres to the nozzle. The spatter is made-up of the elements found in both the piece being welded, and the welding wire, e.g. iron, aluminum and silicon. The instant you stop the weld, the shielding gas dissipates leaving this semi-molten material exposed to the atmospheric gases, mainly oxygen. The oxygen reacts chemically to the molten steel, allowing iron and aluminum oxides to form on the inside bore of the welding nozzle. These highly abrasive materials are ground into the surfaces of the nozzle during cleaning, causing the nozzle to degrade rapidly.
As indicated above, a common problem to each of these basic welding processes is weld spatter. One widely used solution throughout the MIG welding industry is to secure a copper welding nozzle to the torch body. The problem with copper welding nozzles is that during the welding process, molten metal or weld spatter, which can reach a temperature of 10000.degree. F. or more, impacts and etches the copper. The constant bombardment of weld spatter erodes the copper and allows the spatter to adhere to the nozzle. Once spatter begins to attach to the nozzle, it will continue to buildup and eventually restricts the flow of shielding gas to the weld. The result is a flawed weld.
Usually a flawed weld occurs before the spatter buildup is detected. As a result, the welded item is rejected and must be either discarded or rewelded, which is time consuming and increases the cost of manufacturing the item. To correct the problem, the operator typically removes the copper nozzle from the welding torch and dislodges the spatter by scraping it off with a sharp metal edge of a tool such as a screwdriver or chisel. Cleaning the copper nozzle in this manner usually reduces the working life of the nozzle because deep scratches and gouges are left by the cleaning tool. In addition, after the nozzle has been subjected several times to spatter removal in this manner, its ability to obstruct spatter buildup diminishes.
Copper nozzles also present a problem because copper is classified as a hazardous material and cannot be discarded in ordinary landfills. Thus the copper nozzles are not easily disposed of and must be recycled. A more significant problem with the use of copper nozzles is the generation of smoke. The smoke results from an anti-spatter compound which is applied to the copper nozzle to inhibit the buildup of weld spatter. When the compound is subjected to the high temperatures associated with welding, smoke is generated. For environmental reasons, it is desirable to reduce the amount of smoke which is generated by most industrial processes.